Skip to main content

Full text of "Circuits"

See other formats

PS/2/You LED Sign 

Make] Projects 

PS/2/You LED Sign 

Written By: Immanuel McKenty 


Chisel d) 

Computer with internet connection and 

USB port (1) 

Desolderina braid or solder sucker (1) 

Drill and bits: 5/64", countersink (1) 


Glue gun and hot glue (1) 

Hammer or mallet (1) 

Handsaw or chop saw d) 

Measuring tape or long ruler (1) 

Multimeter d) 

Needlenose pliers (1) 

(optional) handv for pluaaina in 

breadboard jumpers 

Screwdriver, medium d) 

Solderina iron and solder (1) 

Table saw (1) 


Wire cutters d) 


Make PS/2/You Kit (1) 

from the Maker Shed 

( Our kit 

includes almost evervthina you need to 

build your own PS/2/You sian except for 

the enclosure. 

Dot matrix LED display modules, 8x32, 

with ribbon cable (3) 

Sure Electronics item #DE-DP106. about 

$9. or odule. This item was 

recently discontinued but is available on 


Computer keyboard with PS/2 

connection (1) 

Thev're readily available at thrift stores. 

You can also use a USB keyboard with a 

USB-to-PS/2 adapter. 

Ardweeny microcontroller (1) 

This small, cheap Arduino clone fits into 

a standard 14-pin DIP socket, but it 

doesn't come with an onboard 5V voltaae 

) Make Projects 

Pagel of 18 

PS/2/You LED Sign 

regulator or an FTDI USB-serial 

converter for programming. 

5V voltage regulator (1) 

You can use a 7805, but the low-dropout 

LM2937 will make your batteries last 

longer, especially with lower-voltage 


PS/2 port (1) 

from an old PC motherboard: ask your 

local computer shop. 

Breadboard (1) 

Breadboard jumper wires, or solid core 

22AWG wire (20) 

(around 20. multiple colors) Jumpers are 

easier to use and well worth the 

FTDI serial programmer (1) 
such as the FTDI Friend. Maker Shed 
#MKAD22. $15 
• AC wall adapter (1) 

can be found for $1-$2 at most thrift 


DC power jack (1) 

which ever matches your adapter 

Power switch (1) 


Capacitor (1) 

Batteries (6) 

Battery holder (1) 

Battery holder (1) 

in a long, flat 2x2 configuration 


4' total 

) Make Projects 

Page 2 of 18 

PS/2/You LED Sign 

Electrical tape or heat shrink tubing (1) 

Acrylic/plegixglass sheet (1) 

Lexan will work great but is more 


Wood screws (8) 

1 1/4" long 

Wood screws (6) 

1/2" long 

Wood screws (12) 

1/2" long (optional) 

Dimensional lumber (1) 

(3/4" x 3 1/2"). 4' length, or 1x2 (3/4" x 

13/4") . 8' length 


It all started with a small LCD salvaged from an old printer. I recruited my code-savvy older 
brother, Adam, and we soon had the LCD displaying text from an Arduino microcontroller. 
This was neat, but it was inconvenient having to plug the Arduino into a computer for 
reprogramming whenever we wanted to change the text. 

We needed something for inputting the text, and it didn't take long to find a PS/2 keyboard 
code library for Arduino — which confirmed my observation that anything that communicates 
with wires has probably been hooked up to an Arduino. I salvaged a PS/2 port from an old 
computer motherboard, and after some trial and error, we could plug in a common PS/2 
keyboard ($5 new) and type messages directly into the Arduino and out to the LCD. 

The LCD was so small, however, that hardly anyone noticed our witty remarks. We needed a 
bigger display. After looking at many appallingly priced commercial LED matrix products, we 
found a new and much cheaper offering: 

Sure Electronics' 8x32 display boards. They cost $9 each and you can cascade up to four 
into one long display. We ordered three, and by the time they'd arrived, the Arduino 
community had already produced a library to run them. (Our code is based on two open 
source Arduino libraries: PS2Keyboard, by Christian Weichel; and MatrixDisplay, by Miles 

) Make Projects 

Page 3 of 18 

PS/2/You LED Sign 

Burton.) The result is our PS/2/You system, which displays keyboard-typed messages in 2"- 
tall LED letters that can be read from quite a distance. You can store and switch between six 
different lines of text, and it automatically scrolls through lines that are too long for the 
display. Power comes from an AC adapter or six AA batteries for portable operation, and the 
whole thing is housed in a sturdy wooden frame. 

Step 1 — Build the frame. 

• Cut the 1 x4 lumber in half lengthwise to make 2 strips about 3 A"xWa" (a nominal 1 x4 is 
actually around 3 A"x3V2"). Use a narrow-kerf blade if possible. 

• Line up the 2 boards beside each other on a flat surface with their narrow edges up. Place 
one of the display panels facedown between the boards, so that the flanges on the panel 
rest on the boards, with the protruding LED matrix between them. Gently squeeze the 
boards snug against the sides of the LED matrix, and measure between the outside edges 
of the boards. This measurement is the length of the frame's end pieces. (Remember this 
measurement for the following steps.) 

• Use a chop saw or handsaw to cut a 45° angle on one end of each piece, oriented so the 
cut goes diagonally across the narrow edge. Measure 18 1 /4 M down the board's length from 
the inner edge of the cut, and make a second 45° cut that angles back out. Repeat on the 
second board. These will be the 2 long sides of the frame. 

) Make Projects 

Page 4 of 18 

PS/2/You LED Sign 

Step 2 

• On each of the leftover board pieces, mark the distance measured measured in Step 1 
down from the sharp, outside edge of the miter cut, along the longer face of the board. Cut 
one at 45° angled in from the measured length (the mirror image of the first cut), which will 
be each piece's longest dimension. Don't cut the other piece yet. 

• Desolder the PS/2 port from its donor motherboard. Line up the DC jack, PS/2 port, and 
power switch atop the edge of the marked but uncut short piece of wood. Mark out a notch 
in the edge of the board just wide enough for all of them to fit next to each other and deep 
enough that the tallest component will sit flush. 

• With a handsaw (or chop saw) cut the 2 edges of the notch. Make a few cuts to the correct 
depth in the middle of the notch, then chisel out the rest of the wood and file the bottom of 
the notch smooth. The ports and switch should slide into the notch easily but without extra 
space. Cut the second (notched) end piece just like the first mitered end piece. 

• NOTE: The frame style isn't crucial, so let your creativity (and materials) have a 
say in the design. I had a woodshop at my disposal, so I made something like an 
extra-deep picture frame with mitered corners and a slot cut in the long sides to hold the 
display panels. 

) Make Projects 

Page 5 of 18 

PS/2/You LED Sign 

Step 3 

• Set the blade of your table saw to a depth of 5/16" (the size of the flanges on the display 
panels). Cut a groove lengthwise down the inside face of each long frame piece, Vi" in 
from the edge (preferably with a narrow-kerf blade). 

• Slide the 3 display panels into the slots in the long frame pieces, all oriented so that the 
writing on the printed circuit boards reads right side up as you look into the back of the 
frame. Fit and hold a frame end piece in place at each end, then drill 5/64" pilot holes and 
countersinks for the VA" #8 screws that hold the frame together. 

• The notched end belongs on the left side of the frame as you read the circuit board backs, 
which is the right side as you view the front of the display. Put the screws in as you go to 
keep the frame together. Ensure that your countersinks are deep enough, and (to avoid 
splitting the frame pieces) don't overtighten the screws. The frame is now finished! 

) Make Projects 

Page 6 of 18 

PS/2/You LED Sign 

Step 4 — Cut the back cover. 

• Place the assembled frame on top of the plexiglass sheet. Use a screw or other sharp 
object to scratch a mark around the edge of the frame. 

• Cut out the back cover with a handsaw, table saw, or the cutting implement of your choice. 
Line up the cut piece on the back of the frame and drill 6 pilot holes through the back cover 
material and into the frame itself. It's now ready to be closed up once all the electronics 
are in place and functioning. 

) Make Projects 

Page 7 of 18 

PS/2/You LED Sign 

Step 5 — Wire the power and PS/2 ports. 

• Wire the 2 battery packs in series by soldering the red (+) lead of one to the black (-) lead 
of the other. 

• Position the battery packs in the frame (I put them at the end opposite the notch), and 
lengthen the remaining 2 wires if necessary by splicing in stranded wire to let them reach 
the notch, where you'll connect them to the DC jack and power switch. Insulate 
connections with electrical tape or heat-shrink tubing. 

• NOTES: The battery packs need to be removable for battery changes, so you can 
secure them in the frame using velcro, although the back cover and display panels 
seem to hold them in place nicely. 

) Make Projects 

Page 8 of 18 

PS/2/You LED Sign 

Step 6 

• Cut one end off a black breadboard jumper, and strip and tin the wire. Repeat with a red 
jumper. Solder the cut end of the black jumper and the black wire from the battery packs 
onto the DC jack's negative terminal. Solder a short chunk of stranded red wire between 
the DC jack's positive terminal and one of the outside contacts on the switch. Solder the 
cut end of the red jumper to the switch's common terminal, and the battery positive to the 
free outside switch terminal. 

• If all went well, your switch should have an off position in the middle, a battery power 
position to one side, and adapter power on the other. 

• Cut one end off 4 more breadboard jumper wires: red, black, blue, and white (or your 
equivalent). Strip, tin, and solder them onto the positive, negative, data, and clock pins on 
the PS/2 port (see pin diagram), and use a multimeter set to "continuity" to confirm the pin- 
wire connections. 

• NOTES: I used blue for data wires, white for read/write and clock wires, yellow for 
the display panels' "CS" wires, and red and black for power and ground — although 
I accidentally switched blue and white here on the PS/2 port. Having a consistent color 
scheme will make it much easier to figure out what's going on. 


) Make Projects 

Page 9 of 18 

PS/2/You LED Sign 
Step 7 

1 <? K^ 


• Dry-fit the PS/2 port, DC jack, and 
power switch again into the notch 
at the end of the frame. Heat up a 
glue gun and dab a bit of glue on 
each one before quickly pressing it 
tightly into the notch. 

♦ This is admittedly an unorthodox 
way of attaching what would 
normally be PCB or panel-mounted 
components, but it's very strong 
and relatively tidy — a good 
substitute when there's no PCB or 
mountable panel nearby. 

) Make Projects 

Page 10 of 18 

PS/2/You LED Sign 

Step 8 — Configure the display panels. 

• Each LED display panel comes with a ribbon cable and has 2 ports on its backside that the 
cable will connect to. 

• Use 2 of the ribbon cables to chain the 3 panels together end-to-end by their adjacent 
ports. Plug one end of the remaining cable into the port closest to the switch and power 
jack. Fold this ribbon up tightly and use hot glue to attach its free end plug to an inner side 
of the frame, with its holes facing up toward the back of the frame. 

• Each LED display panel has a block of little DIP switches labeled CS1, CS2, CS3, and 
CS4. These switches determine how the microcontroller identifies each panel. The 
PS/2/You code numbers the displays left to right, looking from the front, so turn off all but 
switch 3 on the panel nearest the notch, all but switch 2 on the middle panel, and all but 
switch 1 on the panel at the battery end. 

• To see what these switches do, set them to some other sequence once you have 
your display up and running. 


) Make Projects 

Page 11 of 18 

PS/2/You LED Sign 

Step 9 — Add the Ardweeny. 

^F 1 



«ot » a > caW 

• Plug your Ardweeny into the breadboard straddling the trench, with the green LED near the 
top, taking up the first 14 rows. Plug the voltage regulator into the bottom 3 rows on one 

• Plug the 0.1 F capacitor in between the voltage regulator's input and ground legs 
(typically the sequence is IN-GND-OUT, going left to right looking at the front of the 
regulator, but check your datasheet to be sure). 

• Plug the 10 F capacitor's positive leg in the regulator's output and its negative leg 
(marked with a stripe) into the regulator's ground bus. 

• NOTES: The mini breadboard has 17 rows, each consisting of an electrically 
connected 5-hole bus on either side of a central trench. 

• Peel off the breadboard backing (exciting!) and stick it onto the flat, surface-mount Holtek 
chip on the back of the display panel closest to the switch and ports. 


) Make Projects 

Page 12 of 18 

PS/2/You LED Sign 

Step 10 

- ^ ^^^B 

i % 

v ^ 



« ^^^. 




• Since the voltage regulator's ground bus is getting crowded by now, use a small jumper to 
extend it to an unused bus on the other side of the breadboard. 

• Plug the PS/2 port's power wire into the Ardweeny's power and its GND into the 
Ardweeny's GND bus. Plug the PS/2 port's read/write wire into Ardweeny pin D3 and its 
data wire into Arwdeeny pin D7. 

• Use jumpers to connect your components to the ribbon cable plug glued inside the frame. 
Note that the odd-numbered pins on the 2x8 plug run along the side with the small bump, 
opposite the side that the ribbon comes in. 

• To begin, connect CS2, the first wire on the ribbon (marked in pink) to Ardweeny pin D5. 
Connect CS3, the second wire, to D6, and ribbon wire 3 (CS1) to Ardweeny D4. For the 
display's read/write input, connect ribbon wire 5 to Ardweeny D1 1 , and for the data input, 
connect wire 7 to Ardweeny D10. 

• Finally, connect ribbon wire 15 to Ardweeny ground, and ribbon wire 16 to Ardweeny 
power. (You can also wire power and ground to the buses of the voltage regulator.) 

) Make Projects 

Page 13 of 18 

PS/2/You LED Sign 

Step 11 — Program it. 

• If you haven't already, download 
and install the Arduino IDE 
(integrated development 
environment) from . 
Launch the IDE. 

• To configure it for the Ardweeny, 
which acts just like an Arduino 
Duemilanove, click the menu item 
Tools -> Board -> Arduino 
Deumilanove or Nano 

• Then tell it which USB port you'll 
program the Ardweeny through by 
clicking Tools -» Serial Port and 
selecting the highest-numbered 
COM port (if there's more than 

) Make Projects 

Page 14 of 18 

PS/2/You LED Sign 

Step 12 

• Download the code package PS2You and unzip it. 

• Move the PS2Keyboard and MatrixDisplay folders into your Arduino libraries directory. 

• Restart the Arduino IDE and open up the code file PS2You.pde. Connect your computer to 
the Ardweeny with the FTDI programming adapter. Click Verify and Upload, and if all is 
well, a moment later the display will light up with the default text. 

• Unplug the programmer, load some batteries into the battery packs (if you're going to be 
using battery power), and screw on the back cover. You're all set! 

• UPDATE: If you are trying to make the PS/2/You with the new version of the LED 
panels, all you need to do is change line 131 of the MatrixDisplay. ccp file: 

Original code: writeDataBE(8,HTi6 32_CMD_coMSio,true) ; New code for ht1632c 

LED panels: writeDataBE(8,HT1632_CMD_COMS00,true) ; 

• UPDATE 2: If you are using the newest version of the Arduino IDE (1 .0), you will need to 
edit MatrixDisplay. h, Display Toolbox. h, and PS2Keyboard to replace #inciude 

<WProgram.h> and #include <wiring . h> with #include <Arduino . h>. In 

PS2You.pde/.ino, you will also need to change line 141 from textLines [ currentLine ] 

+= c; to textLines [currentLine] += char(c);. 


) Make Projects 

Page 15 of 18 

PS/2/You LED Sign 

Step 13 — Input and Output Modes 

• The PS/2/You has an Input mode 
for entering text and an Output 
mode for displaying it. Pressing 
any alphanumeric key puts the 
system into Input mode, and hitting 
Enter gets you back to Output 

• In Input mode, the PS/2/You 
displays a single line of text as you 
type it in, a maximum of 100 
characters long. You can store up 
to 6 lines of text (this number is 
settable by changing the value of 
numLines near the beginning of 
PS2You.pde). Use the up and down 
arrow keys to select which line to 
edit, and backspace over any line 
of text or hit Escape to delete it. 

• In Output mode, the display loops 
through the stored text lines on its 
own, displaying each for one 
second, or if the line is longer than 
16 characters, it will scroll across 
the display before moving onto the 
next line. If only one line of text is 
stored, it displays continuously. 

) Make Projects 

Page 16 of 18 

PS/2/You LED Sign 

Step 14 — Text Messaging 

_ \ 



1 i .< . 


• The uses for this contraption are 
many. Plug the keyboard in and 
enjoy putting your wittiest 
"wiseclacks" on it in the safety of 
your home, shop, or office — or 
use the battery option to take it into 
the wide world. We like to have the 
keyboard accessible so that 
passersby can add a riposte or two 
to the dialogue. But if monologue is 
more your thing, you can always 
keep the keyboard out of reach. 

• Add a dowel as a removable handle 
so you can wander the streets 
digitally promoting your geekified 
political leanings. Keep score (or 
heckle) at sporting events, deliver 
birthday greetings, advertise your 
wares at a farmer's market, beam 
cryptic messages to your 
neighbors — the possibilities are 

) Make Projects 

Page 17 of 18 

PS/2/You LED Sign 

Step 15 — Further Illuminations 

• There's plenty of room for 
improvement to the code. Try using 
Ctrl and other keys to modify how 
the text displays: flashing, sliding 
in from the top, fading in, or other 

• Four display panels can be 
cascaded together for a longer 
display, and Sure Electronics sells 
an identically programmable 8x32 
panel with 5mm instead of 3mm 
LEDs, so a jumbo PS/2/You is 
almost inevitable. 

Step 16 — Roll your own glyphs. 

• The display font is defined by hexadecimal values in the font.h file. It's not user-friendly for 
editing, but Brent Morse has made a free applet that lets you design your own 5x7 LED 
display glyphs ( htm ) . 

• Use it to modify the font, or make custom smilies or any other pattern you like. 

This project first appeared in MAKE Volume 27 . page 92. 

last generated on 2012-10-31 01:30:33 PM. 

) Make Projects 

Page 18 of 18